Healthcare facilities require preparation and administration of very large numbers of parenteral solutions for patients. Such solutions are administered for both nutritional and therapeutic purposes, and thus efficient liquid-handling systems are required for cost-effective preparation of such solutions, and their administration to patients.
To this end, positive displacement fluid pumping devices have been developed for both preparation and administration of parenteral solutions. Such devices permit precise control during pumping of solutions, thus facilitating solution administration and preparation.
U.S. Pat. Nos. 4,639,245, to Pastrone et al., 4,818,186, to Pastrone et al., and 4,842,584, to Pastrone, all of which are hereby incorporated by reference, disclose a positive displacement fluid infusion pumping device and components thereof, which have met with widespread acceptance by the healthcare industry. This pumping system includes a combination of a pump driver and an associated removable and disposable pump cassette. The pump cassette includes a self-contained positive displacement pump device, which is operated by a reciprocable pump plunger or piston of the associated pump driver. The pump driver includes selectively operable valve actuators, which cooperate with valve mechanisms provided in the pump cassette for accurate and highly automated administration and infusion of parenteral solutions.
Commonly-assigned U.S. patent application Ser. No. 07/444,459, filed Dec. 1, 1989, now U.S. Pat. No. 5,064,774 issued Nov. 11, 1991, discloses a solution pumping system generally of the above type, including a disposable pump cassette, and an associated pump driver. The system of this application is particularly configured for automatic compounding and preparation of parenteral solutions, for subsequent infusion to a patient. This application is hereby incorporated by reference.
Solution pumping systems of the above type employ pre-assembled, disposable pump cassettes. Typically, such pump cassettes include a cassette body having juxtaposed front and rear body members, between which is positioned a membrane-like elastomeric diaphragm. The diaphragm cooperates with the front body member to provide valve mechanisms at various inlets and outlets defined by the front body member, with openings in the rear body member exposing the diaphragm for operation of the valve mechanisms by valve actuators of the associated pump driver.
Additionally, the front body member of the cassette defines a pump chamber, which, together with the internal diaphragm, provides the self-contained positive displacement pump of the cassette. The rear body member defines an opening through which a reciprocable pump piston of the associated driver is movable for operating the cassette, whereby liquid can be pumped through the cassette.
To promote efficiency, it is desirable that when pumping systems of the present type are used for compounding and preparation of parenteral solutions, that the systems be operated with relatively high output of liquid flow, without sacrifice of precision. However, experience has shown that operating of such cassettes at relatively high pressures (which pressures can vary in direct relationship to the viscosity of a liquid), to promote efficient use can be problematical. High pumping pressures require a high degree of sealing integrity within the cassette structure, which can complicate efficient manufacture of the cassettes for disposable use.
Additionally, the pump cassette, as well as the associated tubing and other components through which liquid is pumped, is a so-called compliant system. In other words, by virtue of the flexible and resilient nature of the pump cassette diaphragm, the associated tubing, seals, and the like, the entire system exhibits compliance, or flexing, in response to the creation of liquid pressure within the cassette.
As will be appreciated, such compliance complicates precise and accurate pumping of liquids, creating cyclically undulating pressures within the cassette, attendant to operation, which undulations and instabilities must be stabilized for accurate operation. Of course, this requires providing sufficient periods of time for pressure stabilization during each pumping cycle so that pressure instabilities subside, thereby undesirably increasing the length of each cycle. As will be recognized, the degree of compliance exhibited by the system is directly related to the magnitude of pumping pressures created within the cassette, with reduced pressures desirably resulting in reduced system compliance.
The present solution pumping system promotes efficient and precise operation by minimizing peak pumping pressures, while optimizing liquid output.